1. Field of the Invention
The present invention relates to a starter for starting the operation of an internal combustion engine, more particularly, to a dual-end support type starter in which an end of an output shaft that has a pinion is rotatably supported through a bearing.
2. Description of the Related Art
Japanese Patent Publication No. Hei 7-44811 (1995) and Japanese Patent Laid-Open Publication No. Hei 8-158990 (1996) disclose starters for internal combustion engines. First, the starter described in Hei 7-44811 has a sealing structure as shown in FIG. 8. This sealing structure prevents dust, muddy water, or the like from entering a motor (not shown) through an opening 120 formed through a nose portion 110 of a housing which covers the outer circumference of a pinion 100. The sealing structure is established by fixing a ring-shaped sealing member 130 onto an inner circumference of the nose portion 110 and then bringing an inner diameter portion of the sealing member 130 into contact with an outer circumferential surface of a cylindrical portion 140 provided on the motor side of the pinion 100 in the axial direction (on the left in FIG. 8).
In the starter described in Hei 8-158990, as shown in FIG. 9, a shutter 210 movable in a cooperative manner with a pinion 200 is placed on the side of the pinion 200, the side being opposite (on the left in FIG. 9) to the motor. The shutter 210 closes an opening formed in a nose portion 220 when the starter is stopped, thereby preventing dust, muddy water, or the like from entering the motor through the opening. The shutter 210 moves to the left in FIG. 9 together with the pinion 200 to open the opening when the operation of the starter is started, whereby the pinion 200 and a ring gear 230 can mate with each other.
Each of the starters described in the above-described documents is of the dual-end support type in which the end of the output shaft, which is opposite to the motor, is supported by the end of the nose portion through a bearing. Therefore, it is necessary to form the opening, through which the mating portions of the pinion and the ring gear are exposed, in the nose portion. On the other hand, a single-end support type starter which does not require any opening in a housing has been proposed (see Japanese Patent Laid-Open Publication No. 2000-320438).
In the single-end support type starter, a pinion is attached to an end of an output shaft, which is opposite to a motor. A bearing for supporting the output shaft is provided on the side closer to the motor, in an axial direction, than the pinion. Only the pinion and the end of the output shaft for supporting the pinion, which is opposite to the motor, are exposed through the housing. Since it is not necessary to form any opening in the housing in this structure of the single-end support type starter, dust, muddy water, or the like are unlikely to enter the motor, thereby providing an excellent seal.
However, since the starter described in Hei 7-44811 ensures its sealing function by bringing the sealing member 130 into contact with the cylindrical portion 140 of the pinion 100, it is necessary to set an axial length of the cylindrical portion 140 to be equal to or larger than a movable distance of the pinion in the axial direction. Therefore, the total length of the starter is inevitably increased by the axial length of the cylindrical portion 140, thereby making its installation into a vehicle more difficult or impossible in some instances.
Moreover, the starter includes a clutch 150 that has a larger outer diameter than that of the pinion 100 on the motor side of the pinion 100 in the axial direction (on the left in FIG. 8). The clutch 150 cooperatively moves on an output shaft 160 with the pinion 100. In addition, when the pinion 100 moves to reach the maximum moving position in the axial direction (the position where the pinion 100 mates with a ring gear not shown in the drawing), the clutch 150 enters the moving range of the pinion 100 in the axial direction. Therefore, it is necessary to provide a space 170 for preventing the interference with the clutch 150, inside the nose portion 110. As a result, an inner diameter of the entire nose portion 110 cannot be decreased in accordance with the outer diameter of the pinion 100. Since the maximum outer diameter of the nose portion 110 is increased by the provided space 170, vehicle installation becomes difficult.
In the starter described in Hei 8-158990, at the start of starter operation when the pinion 200 moves on an output shaft 240 in a direction opposite to the motor to mate with the ring gear 230, the shutter 210 naturally opens the opening to prevent the sealing function from acting. Therefore, there is a possibility that dust, muddy water, or the like might enter the motor through the opening.
Moreover, the opening formed in the nose portion 220 has a radial opening face and an axial opening face 250. On the other hand, the shutter 210 is provided in a planar shape sliding in the axial direction because it is necessary to avoid the collision against the ring gear when the shutter 210 moves on the output shaft 240 together with the pinion 200 in a direction opposite to the motor. As a result, when the starter is stopped, the shutter 210 can close only the radial opening face but not the axial opening face 250 as shown in FIG. 9. Therefore, there is a possibility that dust, muddy water, or the like might enter through the axial opening face 250 to penetrate into the motor, which means that sealing is insufficient.
The starter described in Japanese Patent Laid-Open Publication No. 2000-320438 is of the single-end support type without any opening in the housing. Since it has a different structure from that of the dual-end support type described in Hei 7-44811 and Hei 8-158990, they cannot be compared with each other in the same manner. However, since the single-end support type starter has a longer total length than that of the dual-end support type starter in view of structure, this type is disadvantageous in terms of mounting it in a vehicle.